Liquid phosphorous precursor delivery apparatus

ABSTRACT

The present invention recognizes that the build-up of residue in a metal alloy injection valve used to inject a liquid phosphorous precursor compound is due to the nickel in the alloy affecting the liquid phosphorous precursor compound. The invention thus provides components manufactured of an alloy having a low nickel content, preferably less than 5% nickel, and more preferably less than 1%. In an additional aspect of the invention, the alloy is provided with a higher chromium content, preferably at least 15% chromium, more preferably 16-27%.

BACKGROUND OF THE INVENTION

The present invention relates to delivery systems for liquid phosphorousprecursors, and in particular to stainless steel containers, piping andinjection valves for injecting liquid triethylphosphate (TEPO), TMP orTEP into a chemical vapor deposition (CVD) chamber.

A variety of different systems can be used to deliver processing gasesto a chemical vapor reaction chamber. In a boiler system, the liquid isheated into vapor form. In a "bubbler" system, gaseous helium isintroduced into a liquid in a container, resulting in some of the liquidbeing bubbled out of solution. When the liquid contains a phosphorousprecursor, such as TEPO, TMP or TEP, and the container or piping isstainless steel, residue build-up has been observed, in particular wherethe stainless steel is exposed to heat.

Injection valves are often used for providing a processing gas to a CVDchamber. In one method of doing this, the active gas component isprovided in liquid form to an injection valve. The injection valveprovides the liquid through an orifice past which a carrier gas isprovided. A pressure drop is created which causes the liquid to vaporizeinto gaseous form. Typically, a heater is also provided on the valve toprevent condensation of the processing gas. A typical inert carrier gasis helium.

One problem encountered with such valves is the build-up of residuearound the orifice, which can prevent proper seating of a cut-off plugto hinder control of the valve. Excessive build-up of residue can alsoblock the orifice itself, or severely restrict the flow of liquidthrough the orifice. Residue build-up on other surfaces can contaminatesubsequent gases flowing across the surface or contained in thecontainer.

Accordingly, it would be desirable to have an liquid phosphorousprecursor delivery system which minimizes the build-up of residue onstainless steel surfaces.

SUMMARY OF THE INVENTION

The present invention recognizes that the build-up of residue in a metalalloy injection valve used to inject a liquid phosphorous precursorcompound is due to the nickel in the alloy affecting the liquidphosphorous precursor compound. The invention thus provides componentsmanufactured of an alloy having a low nickel content, preferably lessthan 5% nickels and more preferably less than 1%. In an additionalaspect of the invention, the alloy is provided with a higher chromiumcontent, preferably at least 15% chromium, more preferably 16-27%.

The chromium appears to inhibit the leaching of the metal by the liquidphosphorous precursor compound, thus preventing the nickel being leachedout of the metal to affect the liquid phosphorous precursor compound.The nickel appears to act as a catalyst for causing decomposition of thephosphorous precursor compound when heated. Preferably, the componentsexposed to the phosphorous precursor compound and heat are made ofstainless steel alloys of standard industrial designations 430, 440, or446, which all have a nickel content of less than 1%.

In one embodiment, an injection valve is made of stainless steel alloysof standard industrial designations 430, 440, or 446. This alloy ispreferably used for the body of the valve, but in particular for atleast the portions of the valve around the injection orifice.

In another embodiment, a polyamide is used for a plug in an injectionvalve instead of prior art fluoropolymers. The polyamide, preferablyVespel (a 3M product) is used, and exhibits better tolerance to theliquid phosphorous precursor compound and heat. The polyamide can alsobe used for gaskets and seals.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a liquid injection system including aninjection valve according to the present invention;

FIG. 2 is a block diagram showing an injection system having multipleinjection valves, including an injection valve for TEPO according to thepresent invention;

FIG. 3 is a detailed diagram of the injection valve according to thepresent invention; and

FIGS. 4 and 5 are diagrams illustrating the build-up of residue on aninjection valve.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description illustrates one embodiment of the presentinvention using an injection valve system. The invention also applies toboiler and bubbler systems, with the low nickel stainless steel alloybeing used for liquid containers in such systems, or for tubing orconduit, or for any other portion that is exposed to a liquidphosphorous precursor containing compound and also to heat.

FIG. 1 illustrates a basic injection valve system for providing processgases to a process chamber 12. A liquid container 14 containing liquidTEPO 16 is pressurized using helium provided through a valve 18. Thepressurized helium in the top of container 14 forces the liquid TEPO 16through a line 20 to a liquid mass flow meter (LFM) 22 which meters theamount of liquid provided to an injection valve 24 via an injection line26. The injection valve is also provided with a carrier gas, preferablyhelium, through a mass flow controller (MFC) 28 and a carrier gasinjection line 30. Injection valve 24 converts the liquid from injectionline 26 into gaseous form, and provides it along with the carrier gasthrough an outlet line 32 to process chamber 12. Process chamber 12includes a monitoring pressure sensor 34 and a vacuum pump 36 forremoving exhaust gases.

FIG. 2 illustrates the application of multiple gases to chamber 12,including the liquid TEPO provided through injection valve 24. In FIG.2, there is also shown a control valve 38 for liquid TEPO connected to acontrol valve 44 allowing purging of the gas lines with nitrogen (N₂).

FIG. 2 shows injection valve 24 being connected to a common gas line 42connected to process chamber 12. Also included in gas line 42 are aninjection valve 44 for liquid TEOS and an injection valve 46 for liquidTEB. Injection valve 44 has associated with it a liquid flow meter 48and valves 50 and 52 for controlling the liquid TEOS and nitrogen purge.A degasser 51 may optionally be included to remove helium, where heliumis used to pressurize the TEOS (degassers may be used in other gas linesas well). Similarly, injection valve 46 is connected to a liquid flowmeter 54 and associated valves 56 and 58 for controlling the liquid TEBand nitrogen. Finally, mass flow controllers 60 and 62 connect to gasline 42 providing a low flow carrier, and high flow carrier,respectively. Preferably, helium is typically used as the carrier.

FIG. 3 shows injection valve 24 in more detail. The TEPO liquid isprovided through liquid mass flow meter 22 via inlet line 26. The inletline is connected to a chamber 64 which includes a spring 66 for biasingagainst a plug 68. Plug 68 is moved in and out under processor controlin order to control the amount of flow of liquid TEPO. The top ofchamber 64 is a gas orifice 70.

Helium is provided as a carrier gas through an inlet line 30, and thecombination gas mixture is provided through an outlet line 32 to theprocess chamber. The gas flow of the helium over the orifice causes apressure drop which causes the liquid TEPO to vaporize, and be carriedwith the helium through outlet line 32 to the process chamber.Necessarily, orifice 70 is small in order to aid this vaporizationprocess, and thus is vulnerable to residue build-up. Prior art valvestypically include a valve body, including the portion surrounding theorifice, made of a stainless steel alloy. For example, stainless steelalloy SST 316 is used in prior art valves manufactured by Lintec ofJapan.

Plug 68 in existing valves is a compressible sealer typically made ofKel-F (a 3M fluoropolymer). We have found that Kel-F tends to swell upand break. Accordingly, another aspect of the present invention is theuse of Vespel (DuPont polyamide resin) for the plug. Vespel can also beused for gaskets and seals in any system which utilizes a liquidphosphorous precursor compound.

The valve also includes a shut-off plug 72 which can be lowered to closethe orifice when flow is desired to be shut off. Plug 72 is alsopreferably made of Vespel. Also included are heater elements 74 whichfunction to heat the valve to prevent condensation of the gaseousmixture. A thermal couple 76 allows monitoring of the temperature of thevalve.

FIG. 4 illustrates a residue build-up 80 around orifice 70 to a level of300μ. This build-up does not substantially affect the flow of gas out ofthe orifice, but does impact the proper seating of shut-off plug 72 whenit is desirable to stop the flow of TEPO.

FIG. 5 illustrates a build-up of residue to a thickness of 1800μ, whichclogs the orifice itself, as shown by residue 82 in FIG. 5. As can beseen, orifice 70 is completely clogged at this point. Typically, theorifice itself has a diameter of 2 mm.

The inventors of the present invention determined through a series oftests that the presence of nickel in the stainless steel alloy of thevalve around orifice 70 was affecting the liquid TEPO, causing theresidue build-up. The prior art valves using the stainless steel alloyof SST 316 would typically contain approximately 12-15% nickel, and16-18% chromium. In an experiment, a valve made of a stainless steelalloy 430, which contains approximately 0.15% nickel and 16-18% chromiumwas used. The use of such a valve allowed TEPO to flow for 189 hours(equivalent to a throughput of 11,300 wafers). The prior art valve usingthe 316 alloy, on the other hand, has been typically observed to have athroughput of 1800 wafers prior to clogging due to residue build-up. Onthe other hand, the 430 test still had no significant residue build-upafter 189 hours, suggesting that a much longer lifetime was stillavailable to the valve. The build-up of the residue which has beenobserved may be due to the nickel helping to decompose TEPO intophosphoric acid and ethanol. This can be avoided by limiting the amountof nickel in the alloy. In addition, the presence of chromium inhibitsthe leaching of the nickel out of the metal by the TEPO liquid. Alloyswith a higher chromium content are preferred, but may be more expensive.Alloy 446, for instance, has approximately 0.6% nickel and 23-27%chromium. Alloy 440 has 0.6% nickel and 16-18% chromium.

In addition, by empirical observation, it was determined that atemperature of approximately 160-170° C., preferably 165° C., for thevalve provided an optimum flow of the TEPO liquid, avoiding residuebuild-up.

The TEPO liquid, used for generating phosphorous precursor gas, istypically used for the BPSG (Boronphosphosilicate glass) and PSG(phosphosilicate glass) process steps in the processing of a wafer.

As will be understood by those with skill in the art, the presentinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. For example, stainlesssteel alloys having a higher chromium content or lower nickel contentcould be used. Additionally, the valve could have an appropriate alloyof stainless steel only around the sensitive orifice area of the valve.The low nickel stainless steel alloy could also be used for stainlesssteel gaskets. Alternately, a different type of processing system, suchas a distillation system with a stainless steel column that comes incontact with a liquid phosphorous precursor compound and heat, could usethe present invention. Accordingly, reference should be made to theappended claims for describing the scope of the present invention.

What is claimed is:
 1. An apparatus comprising:a sealer in contact with a liquid phosphorous precursor compound; said sealer being a polyamide.
 2. The apparatus of claim 1 wherein said phosphorous precursor compound comprises TEPO, TMP or TEP.
 3. The apparatus of claim 1 wherein said sealer is a shut-off or control plug in a valve.
 4. The apparatus of claim 1 wherein said sealer is a gasket.
 5. An apparatus for delivering a liquid phosphorous precursor compound, comprising:a container for holding said liquid phosphorous precursor compound; a conduit for delivering said liquid phosphorous precursor compound or a gaseous product of said liquid phosphorous precursor compound; wherein at least a portion of said container or said conduit includes a sealer composed of a polyamide.
 6. The apparatus of claim 5 wherein said sealer is a shut-off or control plug in a valve.
 7. The apparatus of claim 5 wherein said polyamide is Vespel.
 8. The apparatus of claim 5 wherein said apparatus is a bubbler system for delivering gases to a chemical reaction chamber for semiconductor wafers.
 9. The apparatus of claim 5 wherein said apparatus is a boiler system for delivering gases to a chemical reaction chamber for semiconductor wafers.
 10. The apparatus of claim 5 wherein said apparatus is an injection system for delivering gases to a chemical reaction chamber for semiconductor wafers, and wherein said sealer is a plug in an injection valve.
 11. The apparatus of claim 5 wherein said sealer is a gasket.
 12. The apparatus of claim 5 wherein said phosphorous precursor compound comprises TEPO, TMP or TEP.
 13. The apparatus of claim 5 wherein a portion of said container or said conduit is composed of a stainless steel alloy having less than 5% nickel.
 14. An liquid flow injection valve for supplying a liquid phosphorous precursor source to a chemical vapor deposition (CVD) chamber comprising:a container of said liquid phosphorous precursor, said liquid phosphorous precursor being one of TEPO, TMP or TEP: an injection orifice for connecting to said container; and a valve outlet for delivering a gaseous mixture generated from said liquid phosphorous precursor compound to said CVD chamber; a shut-off or control plug in said valve, said plug being composed of Vespel.
 15. A liquid injection system for a CVD chamber comprising:a container for holding liquid phosphorous precursor compound, said liquid phosphorous precursor compound being one of TEPO, TMP or TEP; an injection valve for converting said liquid phosphorous precursor into gaseous form, said injection valve having portions in contact with said liquid phosphorous precursor compound composed of a stainless steel alloy having less than 5% nickel and at least 15% chromium; a shut-off or control plug in said injection valve, said plug being composed of a polyamide; a liquid phosphorous precursor compound injection line coupling said container to said injection valve; a carrier gas source line coupled to said injection valve; and an outlet line coupling said injection valve to said CVD chamber. 